U.S. Patent Publication No. US2011/0028004, which is incorporated herein by reference in its entirety, discloses a mark used in the determination of overlay error and comprises sub-features, the sub-features having a smallest pitch approximately equal to the smallest pitch of the product features. The sensitivity to distortions and aberrations is similar as that for the product features. When the mark is developed the sub-features merge and the outline of the larger feature is developed.